الفهرس Only 14 pages are availabe for public view
 |  | from | 184 |  |  |
| | | from | 184 | | |
Abstract
This experiment was conducted to examine the effect of dietary methionine, folic acid and B12 levels and their interactions on laying hen performance, immunity, egg quality and economic efficiency. The experiment was conducted in a 3 x 3 x 2 factorial arrangement of treatments, where three levels of methionine (0.40, 0.45 and 0.50 %), three levels of folic acid (6.0, 9.0 and 12.0 mg/kg) and two levels of B12 (0.01 and 0.02 mg/kg) were used. Nineteen experimental diets (the previous 18 diets in addition to the control diet) were formulated using linear programing to be isocaloric (2784 k.cal ME/kg) and isonitrogenous (18.58% CP) according to the recommended allowances of the Bovans White breed. The control diet contained 0.45% methionine, 0.50 mg folic acid/kg and 0.01 mg cyanocobalamin /kg. The diets were fed to 1824 Bovans White laying hens, 28 weeks of age for 16 wks, which were, divided randomly into 19 treatments, of 96 hens each, in 4 replicates.
The results of this study showed that egg production rate was not significantly affected by the studied levels of methionine, folic acid or B12, however 0.50% methionine resulted in better production rate than 0.40 or 0.45%. The amounts consumed of methionine, folic acid and B12 under the experimental condtions were ranged between 418-538 mg/h/d, 0.61-1.28 mg/h/d. and 1.03-2.16 µg/h/d, respectively without any advers effect on the laying hen performance or the body weight. Feed conversion ratio was improved with increasing methionine level, being the best at 0.50% methionine level. Feed conversion ratio values of treatments contained high methionine level with folic acid and B12 supplementation were better compared with other treatments and control diet, however the difference was not significant between the control and the best value of T15 (1.97 vs. 1.86). Increasing both methionine and folic acid levels increased shell weight, especially during the 1st period, while increasing B12 level almost had no effect.The experimental treatments had no adverse effect on antibody titters, blood heamoglubin content or the digestibilities of the nutrients as compared with the control. It is concluded that although the highest economic efficiency of Bovans White laying hens from 28 to 43 wks of age (about 20% more than the control) was for the diet containing 12.0 mg folic acid/kg and 0.02 mg B12/kg in addition to high methionine level (0.50%), the laying hen performance parameters were not significantly different than the control (the diet containing 0.50 mg folic acid/kg diet and 0.01 mg B12/kg in addition to 0.45% methionine).